In facsimile transmission, the largest operating cost is typically the cost of transmission time over the communication link. This problem is usually addressed by compressing the video data before it is transmitted. Another more hidden cost in facsmile transmission is the time consumed by the facsimile receiver in producing the finished copy of the transmitted image. This hidden cost shows up in the cost per copy of operating the system. To reduce the per copy cost of the facsimile system, it is very desirable to increase the system's throughput (number of documents processed per unit time).
These problems may be attacked by reducing the amount of raw video data from the scanner and by printing reduced copies of multiple originals on a single page at the printer. By reducing the amount of raw video data to be processed, the transmission time is greatly reduced. By printing multiple, reduced copies on one page at the receiver, the apparent resolution is maintained, despite a reduction in video data, and the throughput of the facsimile system is substantially increased. However, apparatus for producing multiple reduced copies on one copy page in a facsimile system does not exist.
Changing the size of the printed image at a receiver relative to the scanned original at the transmitter is well known. Some of the older techniques for doing this used mechanical linkages or variable speed motors to change the magnification or reduction ratio between the copy and the original. U.S. Pat. Nos. 3,109,888 and 3,582,549 are examples of such machines.
Size variation between copy and original in facsimile systems can also be accomplished with electronics. There are two types of electronic reduction systems. The first changes the rate at which data is read into and out of a video data storage device. The size change corresponds to the ratio between the frequencies at which data is loaded into and out of the storage device. Examples of machines in this category are shown in U.S. Pat. Nos. 3,272,918, 3,541,245, 4,054,914, and 4,163,605.
The second type of electronic reduction system changes the copy size relative to the original by processing the video data from each picture element (pel) according to video enhancement algorithms. These video data processing systems shrink or extrapolate the print data from the scanned video data. U.S. Pat. Nos. 4,075,663 and 4,124,871 teach such video data processing systems. Even though changing the size of the copy relative to the original is well known, none of the above patents address the problem of producing multiple reduced copies on a single page. There is one U.S. Pat. No. 3,280,252, which teaches scanning multiple originals at a transmitter and engraving their copies on one drum at the receiver. However, there is no reduction in size between the copy and original. If there are two originals on individual scan drums at the transmitter, the engraving drum at the receiver has a diameter twice that of the scan drums and uses two engraving heads. Accordingly, this patent operates in a manner different from the present invention and does not address the problem of printing multiple reduced copies on a single page.
One U.S. Pat. No. 3,233,037, does teach reducing the scanned image of two originals and printing them side-by-side on a single copy document. This patent relates to merging two weather maps. Both weather maps at the sending station are scanned simultaneously. The transmission signal is switched between scanners so that data from one scanner is sent for one line and data from the second scanner is sent for the next line. Alternate lines in each scanned image are dropped out. At the receiver, the print head is operated at half speed. When the alternating lines of transmitted data from both images arrive, one image line is printed on the left half of the copy document and the second image line is printed on the right half of the copy document. This patent does not address the practical problems of printing multiple reduced images at a facsimile receiver based on successive scanned images.